Study On Preparation And Properties Of Epoxy Resin And Its Composites With High Thermal Conductivity

Epoxy resins and its composites with high thermal conductivity,excellent mechanical and good dielectric properties are vital to the operation stability of modern electrical and electronic equipments.Recently,scientists and engineers have paid a lot of efforts to improve the overall performance of epoxy resins and its composites.However,there are still many problems to be solved,such as the preparation of intrinsic thermal conductive epoxy resins with good over-all properties,the interface between fillers and epoxy matrix,the dispersion of fillers in thermal conductive epoxy composites and the poor mechanical properites of epoxy composites with the high filling loading,etc.In order to solve these problems,we prepared successfully two seires intrinsic thermal conductive epoxy resins with bipheny structure in this dissereation by a simple and controllable strategy.The relationship of microstructure structures and the physical properties of intrinsic thermal conductive epoxy thermosets were systematicly studied.Then,the simple,controllable and solvent-free method was used to prepare the funcationalized fillers.By designing of different interface structures,we investigated systematicly the effect of its different interface structures on the physical properties of epoxy composites with high thermal conductivity.At last,epoxy composites with higher thermal conductivity,excellent mechanical and good dielectric properties were successfully prepared.First,in order to obtain the intrinsic thermal conductive epoxy resins with low viscosity,four amino epoxy resins with different chemical structures were synthesized suceesfully by the water solvent strategy.Amino epoxy resins with biphenol structures formed more orderly rigid structures and perfect liquid crystal structures by?-?interaction during curing,they possed the comprehensive performance of higher thermal conductitiy,excellent mechanical and dielectric properties,etc.In this part,amino epoxy resins were characterized by FT-IR and ~1HNMR,the results demonstrated that amino epoxies were prepared successfully.Then,the curing kinetics of amino epoxies was investigated by DSC.At last,the effect of the chemical structures and microstructure of amino epoxy thermosets on the thermal conductivity,mechanical and dielectrical properties of amino epoxy thermosets were also systematicly studied by TGA,DMTA,XRD and other testing methods.Second,in order to improve poor mechanical properties of amino epoxy thermosets and poor storage stability of amino epoxy resins,the modified biphenyl F epoxy resins containing the different contents of biphenyl were synthesized with biphenyl F epoxy resin and 4,4?-dihydroxydiphenyl(DHDP)via the ring-opening polymerization(ROP).The resultes of GPC,FT-IR and ~1HNMR revealed that the modified biphenyl F epoxy resins were prepared suceesfully.Then,the effect of the DHDP content on the microstructure of the modified biphenyl F epoxy thermosets and the relationship of its microstructure and macro over-all performance were investigated by TEM,AFM,DMTA,XRD,broadband dielectric spectroscopy and othertesting methods.The results showed that the modified biphenyl F epoxy thermosets with DHDP content possed nano-structure with long-range order,and they exhibited high thermal conductivity,good thermal stability,high glass state temperature and excellent dielectirc properties.Moreover,the thermal conductivity of the modified biphenyl F epoxy thermosets could be adjusted by changing the DHDP content.Third,in order to further improve the over-all performance of amino epoxy thermosets,the in-situ grafting strategy with solvent-free was used to functionalize halloysite nanotubes(HNTs)for improving the interface between HNTs and epoxy matrix.Firstly,coupling agent(KH 560)was grafted on HNTs surface.Then,two amino chemicals with biphenol structure were grafted to the coupling agent,and the different chemcial structures were existed on the surface of the funcationalized HNTs.The results of FT-IR,~1HNMR,TGA,XRD,BET analysis and other testing methods showed that the funcationalized HNTs were prepared successfully,and the SEM observation results showed that the funcationalized HNTs had the better dispersion in ethanol solution.The epoxy/HNTs composites were prepared by traditional vacuum casting process,and the effect of different functionalized HNTs on the properties of epoxy/HNTs composites was investigated systematicly by SEM,DMTA,broadband dielectric spectroscopy and othertesting methods.The results showed that the functionalized HNTs impoved greatly the thermal,mechanical and dielectric properties of epoxy/HNTs composites,especially for the impact strength and dielectric loss.Lastly,in order to further improve thermal conductivity of the modified biphenyl F epoxy thermosets and interfacial structure of fillers and epoxy matrix,two series functionalized synthetic micas with two chemical layers were developed by dopamine self-polymerization and in-situ grafting strategies.The effect of different interfacial structures on thermal conductivity,thermal stability,dielectric and mechanical properties of epoxy/mica composites was studied systematicly.Compared with the functionalized synthetic micas by in-situ grafting methods,the functionalized synthetic micas by coating polydopamine(PDA)and grafting fluorochemicals in the second layer showed better dispersion in epoxy matix,and the corresponding epoxy composites exhibited more perfect interfacial structures.Therefore,epoxy/mica@PDA@F composties exihibited higher impact strength and lower dielectric loss,at the same time,the dielectric loss and dielectric constant of epoxy/mica@PDA@F composties showed lower frequency dependence.It was surprising that the epoxy composites prepared by the functionalized synthetic mica with two layers(f-mica and mica@PDA@F)showed lower thermal conductivity,It was suggested that the thermal conductivity of the epoxy/functionalized micas composies resulted from the balance of interfacial thermal resistance and perfect interface,which will provide a new insight on the relatioship between the interfacial structure and thermal conductivity of polymer composites.